How do you expand (2x-3)^5 using Pascal’s Triangle?

1 Answer
Jan 26, 2018

32x^5-240x^4+720x^3-1080x^2+810x-243

Explanation:

The binomial theorem states, (x+a)^n=sum_"k=0"^n((n!)/(k!(n-k)!))x^"n-k"a^k

Here, n=5, x=2x,a=-3

(2x-3)^5=sum_"k=0"^5((5!)/(k!(5-k)!))(2x)^"5-k"(-3)^k

When k=0,

((5!)/(0!(5-0)!))(2x)^"5-0"(-3)^0

(120/(1*120))*32x^5*1

=32x^5

When k=1,

((5!)/(1!(5-1)!))(2x)^"5-1"(-3)^1

120/(1*24)*16x^4*(-3)

=-240x^4

When k=2,

((5!)/(2!(5-2)!))(2x)^"5-2"(-3)^2

120/(2*6)*8x^3*9

=720x^3

When k=3,

((5!)/(3!(5-3)!))(2x)^"5-3"(-3)^3

120/(6*2)*4x^2*(-27)

=-1080x^2

When k=4,

((5!)/(4!(5-4)!))(2x)^"5-4"(-3)^4

120/(24*1)*2x*81

=810x

When k=5,

((5!)/(5!(5-5)!))(2x)^"5-5"(-3)^5

120/(120*1)*1*(-243)

=-243

Add each individual answer up. The answer is 32x^5-240x^4+720x^3-1080x^2+810x-243.