3.48²-4×1.24²
=3.48²-(2×1.24)²
=3.48²-2.48²
=(3.48+2.48)×(3.48-2.48)
=5.96×1
=5.96
40×3.5²+80×3.5×1.5+40×1.5²
=40×(3.5²+2×3.5×1.5+1.5²)
=40×(3.5+1.5)²
=40×5²
=40×25
=1000
明白请采纳,
有新问题请求助,