the length of a rectangle is 3cm more than the width the area is 70cm2
Area is equal to the length times the width. Thus, A = L·W. Since L = W + 3 and A = 70 cm2 are both given, the equation then becomes
70 = (W+3)W
70 = W2+3W by distribution.
Next, set the resulting quadratic equation equal to zero, factor, then use the zero-product property to solve for W.
W2 + 3W - 70 = 0
(W+10)(W - 7) = 0
W = -10, 7.
Since it does not make sense that the width is negative, W must be 7 cm. We were given the length of the rectangle was 3 more than the width, so the length, L, must be 10 cm.