Question

# Factorise: 5x2−16x−21

Solution

## We have: 5x2−16x−21 We have to split (-16) into two numbers such that their sum is ( -16) and their product is (-105), i.e., 5×−21. Clearly,  −21+5=−16 and −21×5=−105 5x2−16x−21=5x2+5x−21x−21=5x(x+1)−21(x+1)=(x+15)(x−21)

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