Question

How much should $3xy-4a^2+5b^2+2$ be increased to get $-5+4a^2+2b^2-7xy$?

• A. $8a^2+3b^2-11xy+10$
• B. $8a^2-3b^2-10xy-7$
• C. $9a^2-3b^2-11xy-7$
• D. $18a^2-3b^2-10xy$

Answer 1

Correct option is B. $8a^2-3b^2-10xy-7$

To find what should be added to or increased in $3xy-4a^2+5b^2+2$ to get $-5+4a^2+2b^2-7xy$, we simply have to subtract $3xy-4a^2+5b^2+2$ from $-5+4a^2+2b^2-7xy$.

$\therefore -5+4a^2+2b^2-7xy-(3xy-4a^2+5b^2+2)$

$=-5+4a^2+2b^2-7xy-3xy+4a^2-5b^2-2$

$=4a^2+4a^2+2b^2-5b^2-7xy-3xy-5-2$

$=8a^2-3b^2-10xy-7$