Question

If x= 2+√3 , find the value of 4x cube +2xsquare - 8x +7

Answer 1

x=2+√3
4x³+2x²-8x+7
4(2+√3)³+2(2+√3)²-8(2+√3)+7
4(8+3√3+12√3+18)+2(4+3+4√3)-16+8√3+7
4(26+15√3)+2(7+4√3)-9+8√3
104+60√3+14+2√3-9+8√3
109+70√3
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Answer 2

When x =2+√3
4x^3 + 2x^2 - 8x +7 = 4[2+√3]^3 + 2[2+√3]^2 - 8[2+√3] + 7
--> 4[8+12√3+18+3√3] + 2[4+4√3+3] - 8[2+√3] + 7
--> 4[26+15√3] + 2[7+4√3] - 8[2+√3] + 7
--> 104 + 60√3 + 14 + 8√3 - 16 - 8√3 + 7
--> 109 + 60√3

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