Question

Please help. urgent. calculate the value of: E= x^3+1/x^3 if 1/x+x=4
(picture below)

Answer 1

52

Explanation:

1. We see if we cube both sides of the second equation, then it looks more similar to the first equation (E = x^3 + 1/x^3)

(1/x + x)^3 = 4^3

1/x^3 + 3/x + 3x + x^3 = 64

2. Now we rearrange, because we see x^3 + 1/x^3 in the first equation in this equation

x^3 + 1/x^3 + 3x + 3/x = 64

3. We look at 3x + 3/x and see that it looks like the second equation, so we try factoring it

x^3 + 1/x^3 + 3(x + 1/x) = 64

we know x + 1/x = 4, so 3(x + 1/x) = 12

x^3 + 1/x^3 +12 = 64

4. Now we subtract and get our answer

x^3 + 1/x^3 = 52