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#.