# Maths ALevel Homework help

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#1
Hi, I’m super confused how to do this question on my homework, could someone explain it to me?
In the expansion of (a + 3x)⁸, the coefficent of x² is 32/27 times the coefficent of x⁵. What is the value of a?
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1 week ago
#2
so expand from low powers of x to higher powers as far as the x5 term.

now compare the coefficients of the x2 and x5 terms.
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#3
(Original post by the bear)
so expand from low powers of x to higher powers as far as the x5 term.

now compare the coefficients of the x2 and x5 terms.
we have to do it using binomial theorem and with some formula using factorials and i really don't get it?
0
1 week ago
#4
(Original post by lissishannyn)
we have to do it using binomial theorem and with some formula using factorials and i really don't get it?
You don't need to do the full binomial expansion - just look for the terms with the power you need and calculate the coefficients based on the following formula in red
Last edited by Melvin Guna; 1 week ago
1
1 week ago
#5
so for instance the x3 term....

8C3 * a5 * ( 3x )3....

which is 56*a5*27*x3
1
#6
(Original post by Melvin Guna)
You don't need to do the full binomial expansion - just look for the terms with the power you need and calculate the coefficients based on the following formula in red
thank you so much ive got it now 0
#7
(Original post by the bear)
so for instance the x3 term....

8C3 * a5 * ( 3x )3....

which is 56*a5*27*x3
Thank you I understand it now 1
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