Question

find the coefficient of x in the expansion of ( x + 6 )(x + 7)

Answer 1

Answer:  13

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Explanation:

You can use the FOIL rule to expand out the given expression and you should get $x^2+13x+42$

Or you can follow this set of steps

$(x+6)(x+7)\\\\y(x+7) \ \ \text{ ... let y = x+6}\\\\xy+7y\\\\x( y )+7( y )\\\\x( x+6 )+7( x+6 ) \ \ \text{ ... plug in y = x+6}\\\\x^2+6x+7x+42\\\\x^2+13x+42$

Whichever method you use, the x coefficient is 13.