Let a and b be rational numbers and suppose that (a-b)=4 and a*b=1 . Show that (a+b)^2 = 20.
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hint
Use algebraic substitution and the binomial formulas
(a+b)^2 = a^2+2*ab+b^2(a-b)^2 = a^2-2*ab+b^2Solution
(a+b)^2 = a^2 + 2*ab + b^2 = (a-b)^2 +4*ab = 4^2+4*1 = 16+4 = 20 ◽of course the website has something to do with lean
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