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question:Given that F_{1}(sqrt{3},0), F_{2}(sqrt{3},0) are the foci of the ellipse E: frac{x^{2}}{a^{2}} + frac{y^{2}}{b^{2}} = 1 (a > b > 0), and point P(1, frac{sqrt{3}}{2}) is a point on the ellipse E. (1) Find the equation of the ellipse E; (2) A line l passing through point F_{1} intersects the ellipse at points M and N. Find the equation of line l when the area of triangle F_{2}MN reaches its maximum value.
answer:Solution: (1) From the given conditions, we have begin{cases} a^{2}-b^{2}=3 frac{1}{a^{2}} + frac{3}{4b^{2}}=1 end{cases}, which simplifies to frac{1}{b^{2}+3} + frac{3}{4b^{2}}=1. Solving this, we get b^{2}=1, a^{2}=4, therefore The equation of the ellipse E is frac{x^{2}}{4} + y^{2} = 1; (2) Method 1: If k exists, let the equation of line l be y=k(x+ sqrt{3}). Substituting into frac{x^{2}}{4} + y^{2} = 1, we get (4k^{2}+1)x^{2} + 8sqrt{3}k^{2}x + 12k^{2} - 4 = 0, Let M(x_{1},y_{1}), N(x_{2},y_{2}), then x_{1}+x_{2}=-frac{8sqrt{3}k}{4k^{2}+1}, x_{1}x_{2}=frac{4(3k^{2}-1)}{4k^{2}+1}. therefore The distance d from F_{2} to line MN is d= frac{|2sqrt{3}k|}{sqrt{k^{2}+1}}, MN= sqrt{1+k^{2}} sqrt{(x_{1}+x_{2})^{2}-4x_{1}x_{2}}=4sqrt{1+k^{2}}sqrt{frac{1+k^{2}}{(4k^{2}+1)^{2}}}, therefore S_{triangle F_{2}MN}= frac{1}{2}|MN|cdot d=4sqrt{frac{3k^{2}(k^{2}+1)}{(4k^{2}+1)^{2}}}leqslant 4sqrt{frac{[3k^{2}+(k^{2}+1)]^{2}}{4(4k^{2}+1)^{2}}}=2, When and only when 3k^{2}=k^{2}+1, i.e., k= frac{sqrt{2}}{2}, the maximum value is achieved, At this time, the equation of line l is x-sqrt{2}y+sqrt{3}=0 or x+sqrt{2}y+sqrt{3}=0. If k does not exist, i.e., lperp x axis, then S_{triangle F_{2}MN}= frac{1}{2}|MN||F_{1}F_{2}|=sqrt{3} < 2 (discard), In summary: The equation of line l is x-sqrt{2}y+sqrt{3}=0 or x+sqrt{2}y+sqrt{3}=0. Method 2: Let the equation of line l be x=my-sqrt{3}. Substituting into frac{x^{2}}{4}+y^{2}=1, we get (m^{2}+4)y^{2}-2sqrt{3}my-1=0, Let M(x_{1},y_{1}), N(x_{2},y_{2}), then y_{1}+y_{2}=frac{2sqrt{3}m}{m^{2}+4}, y_{1}y_{2}=frac{-1}{m^{2}+4}. therefore S_{triangle F_{2}MN}= frac{1}{2}times|F_{1}F_{2}|times(|y_{1}|+|y_{2}|)= frac{1}{2}times|F_{1}F_{2}|times(|y_{1}-y_{2}|)= sqrt{3}timessqrt{(y_{1}+y_{2})^{2}-4y_{1}y_{2}} = frac{4sqrt{3}timessqrt{m^{2}+1}}{m^{2}+4}= frac{4sqrt{3}}{sqrt{m^{2}+1}+frac{3}{sqrt{m^{2}+1}}}leqslant frac{4sqrt{3}}{2sqrt{3}}=2, When and only when sqrt{m^{2}+1}=frac{3}{sqrt{m^{2}+1}}, i.e., m^{2}=2, the equality holds, therefore When the area of triangle F_{2}MN reaches its maximum value, the equation of line l is x-sqrt{2}y+sqrt{3}=0 or x+sqrt{2}y+sqrt{3}=0. Thus, the final answers are boxed{frac{x^{2}}{4} + y^{2} = 1} for the equation of the ellipse, and boxed{x-sqrt{2}y+sqrt{3}=0} or boxed{x+sqrt{2}y+sqrt{3}=0} for the equation of line l when the area of triangle F_{2}MN reaches its maximum value.
question:Evaluate the product [ (a10) cdot (a9) cdot dotsm cdot (a1) cdot a, ] where a=2.
answer:To evaluate the product [ (a-10) cdot (a-9) cdot dotsm cdot (a-1) cdot a, ] where a=2, we observe that one of the terms in the product is a-2. Given that a=2, we have: [ a-2 = 2-2 = 0. ] Therefore, the product can be rewritten as: [ (a -10) dotsm (a-3) cdot (a-2) cdot (a-1) cdot a = (a-10) dotsm (a-3) cdot 0 cdot (a-1) cdot a. ] Since multiplying any real number by zero results in zero, the entire product simplifies to: [ (a-10) dotsm (a-3) cdot 0 cdot (a-1) cdot a = 0. ] Thus, the evaluated product is boxed{0}.
question:Let a,b,c be positive numbers such that 3a=b^3, 5a=c^2. Assume that a positive integer is limited to d=1 such that a is divisible by d^6.
(1) Prove that a is divisible by 3 and 5.
(2) Prove that the prime factor of a are limited to 3 and 5.
(3) Find a.
answer:Given the conditions: [ 3a = b^3 ] [ 5a = c^2 ] and the assumption that ( a ) is divisible by ( d^6 ) where ( d = 1 ). # Part 1: Prove that ( a ) is divisible by ( 3 ) and ( 5 ). 1. From the equation ( 3a = b^3 ), we can see that ( a = frac{b^3}{3} ). For ( a ) to be an integer, ( b^3 ) must be divisible by ( 3 ). Since ( b ) is a positive integer, ( b ) itself must be divisible by ( 3 ). Let ( b = 3k ) for some integer ( k ). Then: [ b^3 = (3k)^3 = 27k^3 ] Substituting back, we get: [ a = frac{27k^3}{3} = 9k^3 ] Thus, ( a ) is divisible by ( 3 ). 2. From the equation ( 5a = c^2 ), we can see that ( a = frac{c^2}{5} ). For ( a ) to be an integer, ( c^2 ) must be divisible by ( 5 ). Since ( c ) is a positive integer, ( c ) itself must be divisible by ( 5 ). Let ( c = 5m ) for some integer ( m ). Then: [ c^2 = (5m)^2 = 25m^2 ] Substituting back, we get: [ a = frac{25m^2}{5} = 5m^2 ] Thus, ( a ) is divisible by ( 5 ). Since ( a ) is divisible by both ( 3 ) and ( 5 ), we conclude that ( a ) is divisible by ( 15 ). # Part 2: Prove that the prime factors of ( a ) are limited to ( 3 ) and ( 5 ). 1. From the previous part, we have: [ a = 9k^3 quad text{and} quad a = 5m^2 ] Since ( a ) must satisfy both conditions simultaneously, we equate the two expressions: [ 9k^3 = 5m^2 ] This implies that ( a ) must be a common multiple of ( 9 ) and ( 5 ). The least common multiple of ( 9 ) and ( 5 ) is ( 45 ). Therefore, ( a ) must be of the form: [ a = 45n ] for some integer ( n ). 2. Since ( a ) is of the form ( 45n ), the prime factors of ( a ) are ( 3 ) and ( 5 ). # Part 3: Find ( a ). 1. From the equation ( 9k^3 = 5m^2 ), we need to find integers ( k ) and ( m ) such that this equation holds. We rewrite it as: [ 9k^3 = 5m^2 ] This implies that ( k ) and ( m ) must be chosen such that both sides are equal. Since ( 9k^3 ) and ( 5m^2 ) must be equal, we need to find the smallest ( k ) and ( m ) that satisfy this condition. 2. By trial and error or by solving the equation, we find that the smallest values that satisfy this condition are ( k = 5 ) and ( m = 3 ). Substituting these values back, we get: [ a = 9k^3 = 9 cdot 5^3 = 9 cdot 125 = 1125 ] [ a = 5m^2 = 5 cdot 3^2 = 5 cdot 9 = 45 ] Since both expressions must be equal, we find that the smallest value of ( a ) that satisfies both conditions is ( 1125 ). The final answer is ( boxed{1125} ).
question:The slant height of a cone is 17 cm, and the height from the vertex to the center of the base is 15 cm. What is the number of cubic centimeters in the volume of the cone? Express your answer in terms of pi.
answer:Let the slant height (hypotenuse) be denoted as l = 17 cm, the height from the vertex to the center of the base (one of the legs) be h = 15 cm, and the radius of the base be r cm. We again use the Pythagorean theorem: [ l^2 = r^2 + h^2 ] [ 17^2 = r^2 + 15^2 ] [ 289 = r^2 + 225 ] [ r^2 = 289 - 225 ] [ r^2 = 64 ] [ r = 8 text{ cm} ] Now, we calculate the volume V of the cone using: [ V = frac{1}{3} pi r^2 h ] [ V = frac{1}{3} pi (8^2)(15) ] [ V = frac{1}{3} pi (64)(15) ] [ V = frac{960}{3} pi ] [ V = 320pi ] So, the volume of the cone is boxed{320pi} cubic centimeters.