Find the coefficient of x in the expansion of ( x + x 2 ) 9
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
Nice thought.
The expansion of x in ( x + x 2 ) 9 = x 9 + x 9 5 1 2 + 1 8 x 7 + x 7 2 3 0 4 + 1 4 4 x 5 + x 5 4 6 0 8 + 6 7 2 x 3 + x 3 5 3 7 6 + 2 0 1 6 x + x 4 0 3 2
Change the options... easily you can deduce that the coefficient of x must be an even number, the only such option is 2016.
Log in to reply
Exactly, that's exactly how I figured it out :p .Juz coz i'm lazy
Problem Loading...
Note Loading...
Set Loading...
The ( r + 1 ) th term of the expansion can be given by
T r + 1 = ( r 9 ) x 9 − r { x 2 } r
Here, we see that the exponent of x is 9 − 2 r .
Thus, 9 − 2 r = 1 ⟹ r = 4 .
∴ Coefficient of x is ( 4 9 ) ⋅ 2 4 = 2 0 1 6 .