Question 944715
well they made u = x^2, so 


u^2 - 29u + 100 = (u - 4)(u - 25) = (x^2 - 4)(x^2 - 25)


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you now have (x^2 - 4)(x^2 - 25)


you factor each x^2 - 4 and x^2 - 25 using the difference of squares rule. You will have 4 factors when everything is said and done. I'll let you do this part.