Monday, November 7, 2016

algebra precalculus - Solve the equation sqrt[3]x2+4=sqrtx1+2x3




Solve the equation:
3x2+4=x1+2x3
Things I have done so far:
3x2+4=x1+2x3 Deducting 2 from both sides of equation
(3x2+42)=(x11)+2x4
x2+483(x2+4)2+23x2+4+4=x2x1+1+2(x2)
(x2)(x+23(x2+4)2+23x2+4+41x1+12)=0
+)x2=0x=2
+)x+23(x2+4)2+23x2+4+41x1+12=0()

I don't know how to solve the equation (*).
By the way, I think there must be "smart" way to solve this equation.


Answer



3x2+4=x1+2x3



Let x=t2+1 with t0. Then



3t4+2t2+5t=2t213t4+2t2+5=2t2+t1t4+2t2+5=8t6+12t56t411t3+3t2+3t18t6+12t57t411t3+t2+3t6=0(8t5+20t4+13t3+2t2+3t+6)(t1)=0



Note, for t0, that 8t5+20t4+13t3+2t2+3t+6>0. It follows that the only positive solution is t=1. Hence x=2.


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