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binomial problem (1 Viewer)

dathat

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in the expansion (1+x+kx^2) ^9 the coefficient of x^2 is 0, what is the value of k?
 

Mikes

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how did you get that 9c0 9c2 +9c0 9c1 k from that?
From 9c0(1+x)^9, the coefficient of x^2 = 9c0*9c2 (9c2 is the coefficient of x^2 in the expansion of (1+x)^9). Similarly, the coefficient of x^2 in 9c1(1+x)^8kx^2 = 9c0 which you multiply by 9c1, giving 9co * 9c1.
 

Ekman

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The coefficient of x^2 in and the x^2 in is

then you add those 2 terms together.
Are you sure that its 9c1 * 9c0 * k for the coefficient of x^2 in 9c1(1+x)^8kx^2 ? I know it doesn't matter but it should be 9C1 * 8c0 * k
 

integral95

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Are you sure that its 9c1 * 9c0 * k for the coefficient of x^2 in 9c1(1+x)^8kx^2 ? I know it doesn't matter but it should be 9C1 * 8c0 * k
ahhhh damn you're right,I always screw up little things like that, luckily I won't get the wrong answer.
 

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