C2 Binomial expansion

Self teaching myself A-level maths, and could do with a bit of help.
Does anyone have a method of solving this question?

The coefficient of x^2 in the expansion of (2+ax)^6 is 60. Find possible values of the constant A.
I have expanded the binomial to get the x^2 term, and i got (15)(2^4)(ax^2). But this is incorrect/I don't know where to go from here.
Any help would be greatly appreciated.

Reply 1

wanderlust.xx

You might find it easier to take 2 outside the brackets before you start expanding, so your first term becomes 1 and your whole expansion becomes easier.

When you take the two out, you need to make sure it's to the same power as your brackets, so

(2+ax)^6 = 2^6.(1+\frac{a}{2}x)^6

Just a general tip. See if you get a different coefficient for

x^2

when you do it this way.

Reply 2

BJack

Dizzeee

I have expanded the binomial to get the x^2 term, and i got (15)(2^4)(ax^2). But this is incorrect/I don't know where to go from here.
Any help would be greatly appreciated.

You need to square a as well, so it should be

15 \times 2^4 \times (ax)^2 = 240 \times a^2 \times x^2 = 60x^2

Can you see where to go from here?

Reply 3

Dizzeee

so 240a^2= 60
a^2= 0.25
a= +/_ 0.5
Thats the right answer. Thanks for your help :smile:

Reply 4

BJack

No problemo.

Reply 5

Yu5al132

Original post by Dizzeee

so 240a^2= 60
a^2= 0.25
a= +/_ 0.5
Thats the right answer. Thanks for your help :smile:

I've just started a levels and I've come across that very question. But don't understand your guys method. Can you start your working out from the start

Reply 6

RDKGames

Study Forum Helper

Original post by Yu5al132

I've just started a levels and I've come across that very question. But don't understand your guys method. Can you start your working out from the start

This is a very old thread - responses are unlikely. Please start a new one if you want help.

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