Difference in mathematics means subtraction. Product means multiplication. Sum means addition. Hence difference between (2d)2 and 2d2 implies (2d)2−2d2 NOTE: ln(2d)2 the square (2) is affecting both 2 and d since they are both in a bracket but in 2d2, the square (2) only affects the d. 2d means 2×d 2d2 means 2 times d square, thus 2×d2 d2=d×d Hence 2d2=2×d×d In (2d)2, you can simplify the 2d and when done square the result, thus multiply the result by itself. Since d=3, substitute 3 into wherever you see d and simplify 2d=2×d, but d=3 ⇒2d=2×3=6 (2d)2=(2×3)2=62=6×6=36 2d2=2×32=2×3×3=2×9=18 (2d)2−2d2=36−18=18