How can (a+3)2=a2+6a+9 be derived from the polynomial identity (a−3)2=a2−6a+9? A. Add 12a to both sides of (a−3)2=a2−6a+9.
B. Add 6 to both sides of (a−3)2=a2−6a+9.
C. Multiply both sides of (a−3)2=a2−6a+9 by −1.
D. Substitute −a for a on both sides of (a−3)2=a2−6a+9.