Question

Multiply together:
1. a+b+c, a+b-c.​

Answer 1

$Let (b + c) = x </p><p></p><p>Then (a + b + c) ^{2} = (a + x) {}^{2} = a {}^{2} + 2ax + x { }^{2} </p><p></p><p> = a {}^{2} + 2a (b + c) + (b + c) {}^{2} </p><p></p><p> = a {}^{2} + 2ab + 2ac + (b {}^{2} + c {}^{2} + 2bc) </p><p></p><p> = a {}^{2} + b {}^{2} + c {}^{2} + 2ab + 2bc + 2ca</p><p></p><p>Therefore, (a + b + c) {}^{2} = a {}^{2} + b {}^{2} + c {}^{2} + 2ab + 2bc + 2ca$