I will show you a trick that solves all this kind of problems.
15X^{2 }+ 11X - 56
A quadratic like this can only be factorable, if There exist 2 rational numbers whose Sum is 11, and
their product is - 15 * 56
So we rite 15 * 56 as product of its factor
15 * 56 = 3 * 5 * 7 * 8 = 15 * 56 = 35 * 24 =
Now we see that the difference of 35 and 24 is 11
15 X^{2 }+ 35X - 24X -56 ( break up 11X into 35X- 24X)
5X( 3X +7 ) - 8 ( 3X + 7) , Now 2 terms have common factor of (3X +7 )
( 3X + 7 ) ( 5X - 8 ) This is the final answer.
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