( 2x2 + 3x - 5 ) ( x + 2 ) = ax3 + bx2 + d হলে ac - bd = ?

A 70

B 71

C 72

D 73

Solution

Correct Answer: Option C

দেয়া আছে, ( 2x2 + 3x - 5 ) ( x + 2 ) = ax3 + bx2 + d 

বামপক্ষ,
=( 2x2 + 3x - 5 ) ( x + 2 ) 
= 2x3 + 3x2 - 5x + 4x2 + 6x - 10 
= 2x3 + 7x2 + x - 10 

এখন ( 2x3 + 7x2 + x - 10 ) কে ( ax3 + bx2 + cx + d ) এর সাথে তুলনা করে পাইঃ 

a=2, b=7, c=1 এবং d=-10 

অতএব,
ac - bd
= ( 2×1 ) - 7 × (-10)
= 2 + 70 = 72

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