A)x^{2} =t
4 t^{2} -5t+1=0
D=25-4*4*1=9= 3^{2}
t1=(5+3)8=8/8=1
t2=(5-3)/8=2/8=1/4=0.25
x^{2} =1 x=1 и x=-1
x^{2} =0.25 x=0.5 и x=-0.5
б)t= (2x^{2} -3)
t^{2}-4t-21=0
D=16+84=100= 10^{2}
t1=(4+10)/2=14/2=7
t2=(4-10)/2=6-/2=-3
2 x^{2} -3=7
x= \sqrt{5} и x=- \sqrt{5}
2 x^{2} -3=-3
x=0
d)x^{2} -2=t t^{2}-2t-3=0
D=16= 4^{2}
t1=(2+4)/2=6/2=3
t2=(2-4)/2=-2/2=-1
x^{2} -2x=3
x^{2} -2x-3=0
D=16= 4^{2}
x1=6/2=3
x2=-2/2=-1
x^{2} -2x=-1
D=0
x=-2/2=-1