A:﹣2a+2b=﹣2(a+b)
B:a2﹣2a+4=(a﹣2)2
C:(2a2)3=6a6
D:3a2•2a3=6a5
____(tell) many times, he still repeated the same mistakes.
一束激光射到平面镜上,当入射角是65°时,反射角是____ °。