Maths Question - Binomial expansion - please help?

B)

7p is coefficient of x

21p² is coefficient of x²

7p = 21p²

1 = 3p

p = 1/3

coefficient of x is 7p = 7(1/3) = 7/3

coefficient of x² is 21p² = 21(1/3)² = 7/3

That's how it is done.

You need to refer to Pascal's triangle. If you have a scientific calculator, you can work out the row that you need.

The row containing the 7:

1, 7, 21, 35, 35, 21, 7, 1

You have it right so far, the numbers are just then the mirror image. Obviously the powers of p increases, powers of x decrease.

Coefficient of x = 7p, coefficient of x² = 21p²

So 7p = 21p²

3p² - p = 0

p( 3p - 1 ) = 0

p = 0, or 1/3

p = 1/3 is the only reasonable answer.

Coefficient of x³ = 35p³

35 x (1/3)³

= 35/27

you need to put 7px and 21p^2x^2 equal to eachother, then sub the answer you get (after finding p) back into the original equation and then this will help you find x^3!

since coeff. of x and x^2 are equal, from your answer we have:

7p = 21p^2

p = 1/3

the coeff. of x^3 is

35(1/3)^3 = 35/27