Question

If x*2+1/x*2=7and;find the value of: 7x*3+8x-7/ x*3-8/x​

Answer 1

Answer:

7(x^3 - 1/x^3) + 8(x - 1/x)

Since a^3 - b^3 = (a-b)(a^2 + ab + b^2)

7[(x-1/x)(x^2 + 1 + 1/x^2)] + 8(x-1/x)

7[(x-1/x)(7+1)] + 8(x-1/x)

56(x-1/x) + 8(x-1/x)

(x-1/x)(56+8)

64(x-1/x)

Since (x-1/x)^2=x^2 + 1/x^2 - 2=7-2=5

Therefore x-1/x =√5

64√5