Answers

2016-07-22T06:20:06+08:00
5.) 7x^4+8x^2+1=0;

x^2=y;
7y^2+8y +1=0;

(7y+1)(y+1)=0;
y=-1;
y=-1/7;;

y=-1=x^2
x^4=-1....ans

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