Question

What’s the answer??

Answer 1

Use parentheses for M and N
$(5x {}^{2} + 7x - 4 )- ( - 3 {x}^{2} - 4x + 5)$
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remove parentheses
$5 {x}^{2} + 7x - 4 + 3 {x}^{2} + 4x - 5$
一一一一一
add like terms
$8 {x}^{2} + 11x - 9$