已知(a+2b)=7,(a-2b)=3,求a+4b的值,ab的值?
问题描述:
已知(a+2b)=7,(a-2b)=3,求a+4b的值,ab的值?
答
(a+2b)=7,(a-2b)=3 (a+2b)=a^2+4ab+4b^2=7,(a-2b)=a^2-4ab+4b^2=3,两式相加,a^2+4b^2=5 两式相减,ab=0.5
已知(a+2b)=7,(a-2b)=3,求a+4b的值,ab的值?
(a+2b)=7,(a-2b)=3 (a+2b)=a^2+4ab+4b^2=7,(a-2b)=a^2-4ab+4b^2=3,两式相加,a^2+4b^2=5 两式相减,ab=0.5