问题
选择题
已知a+b=2,则a2-b2+4b的值是( )
A.2
B.3
C.4
D.6
答案
∵a+b=2,
∴a2-b2+4b=(a-b)(a+b)+4b,
=2(a-b)+4b,
=2a-2b+4b,
=2(a+b),
=2×2,
=4.
故选C.
已知a+b=2,则a2-b2+4b的值是( )
A.2
B.3
C.4
D.6
∵a+b=2,
∴a2-b2+4b=(a-b)(a+b)+4b,
=2(a-b)+4b,
=2a-2b+4b,
=2(a+b),
=2×2,
=4.
故选C.