Ta có : \(A=x^2+5xy+10;B=7x^2-5xy+10\)\
\(\Rightarrow C=9A-2B=9.\left(x^2+5xy+10\right)-2\left(7x^2-5xy+10\right)\)
\(=9x^2+45xy+90-14x^2+10xy-20\)
\(=-5x^2+55xy+70\)
Vậy \(C=-5x^2+5xy+70\)
Tham khảo:
Ta có : A=x2+5xy+10;B=7x2−5xy+10A=x2+5xy+10;B=7x2−5xy+10\
⇒C=9A−2B=9.(x2+5xy+10)−2(7x2−5xy+10)⇒C=9A−2B=9.(x2+5xy+10)−2(7x2−5xy+10)
=9x2+45xy+90−14x2+10xy−20=9x2+45xy+90−14x2+10xy−20
=−5x2+55xy+70=−5x2+55xy+70
Vậy C=−5x2+5xy+70