76900÷2400
=769÷24
=720÷24+49÷24
=30+2+1÷24
=32又24分之1
长2ab+3,宽2ab-3
所以面积=(2ab+3)(2ab-3)
=(2ab)2-32
=4a2b2-9
已知x=y^2-4y,求dy/dx
76900÷2400
=769÷24
=720÷24+49÷24
=30+2+1÷24
=32又24分之1
长2ab+3,宽2ab-3
所以面积=(2ab+3)(2ab-3)
=(2ab)2-32
=4a2b2-9