Question

X=4+root15 find x cube -1/x cube

Answer 1

Answer:

Step-by-step explanation:

x=4+rt(15)

1/x=1/(4+sqrt(15))=rationalise the denominator

=4-sqrt(15)

x-1/x=2sqrt(15)

x^2+1/x^2-2=4*15

x^2+1/x^2=60+2=62

x^3-1/x^3=(x-1/x)(x^2+1/x^2+1)

=(2sqrt(15)(63)

=126sqrt(15)