A) 1
B) \[-1\]
C) \[-3\]
D) 4
Correct Answer: B
Solution :
\[(3x-4)\left( 5x+7 \right)=15{{x}^{2}}-ax-28.\] \[15{{x}^{2}}+21x-20x-28=15{{x}^{2}}-ax-28\] \[\Rightarrow \]\[15{{x}^{2}}+x-28=15{{x}^{2}}+ax-28\] \[\Rightarrow \]\[x=-ax\] \[\therefore \]\[a=\frac{x}{-x}=-1\] \[\therefore \]\[a=-1\]
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