If 12x2 - 21x + 1 = 0, then what is the value of 9x2 + (16x2)-1 ?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is Option 3 i.e 417/16.
| Understanding/Application |
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12x2 - 21x +1 = 0 Dividing it by 4x - 3x - 21/4 + 1/4x = 0 3x + 1/4x = 21/4 |
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On squaring both sides - (3x + 1/4x)2 = (21/4)2 9x2 + 1/16x2 + 2(3x)(1/4x) = 441/16 9x2 + 1/16x2 = 441/16 - 3/2 9x2 + (16x2)-1 = (441 - 24)/16 = 417/16 |