If $y=2 x+1$, then what is the value of $\left(8 x^3-y^3+6 x y\right) ?$ |
1 -1 15 -15 |
-1 |
Given, y = 2x + 1 We know that, (a – b)3 = a3 – 3a2b + 3ab2 – b3 = 2x - y = (-1) = (2x - y)3 = (-1)3 = 8x3 - 12x2y + 6xy2 - y3 = -1 = 8x3 - 6xy(2x - y) - y3 = -1 = 8x3 - 6xy × (-1) - y3 = -1 = 8x3 + 6xy - y3 = -1 = 8x3 - y3 + 6xy = -1 Method 2 Put the values of x = 1 and then we get y = 3 Put them in required equation. |