x^4-46x^2+45=0
x^4 - 46x^2 + 45 = 0
Let u = x^2
u^2 - 46u + 45 = 0
This factorises; (u - 1)(u - 45) = 0
So 1) u = 1 2) u = 45
Hence 1) x^2 = 1 so 1a) x = 1 and 1b) x = -1
and 2) x^2 = 45 so 2a) x = sqrt(45) , x = sqrt(9*5), x = 3sqrt(5) and 2b) x = -3sqrt(5)
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