proofs 4U (1 Viewer)

kractus

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also 14c i) and ii) xD. im stuck for i) asI expanded (a+b)^3 >= 0 but idk from there
 

jimmysmith560

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Would the following working help with Question 13 (d)?

From part (i):





Similarly:





Adding (1), (2) and (3) together:





Substituting (4) into (5):



 

Masaken

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also 14c i) and ii) xD. im stuck for i) asI expanded (a+b)^3 >= 0 but idk from there
funny enough, i did this as exact question as part of my school hw a few days ago
14ci - move the RHS onto the LHS, so you can have RTP a^3 + b^3 - (a/c + b/c)abc > 0 (pretend = sign is under the >)
expand the brackets out, then it's a matter of factorising through grouping in pairs, then you can prove the inequality for > 0, then you can do similar for the other two expressions the question asks you to do
14cii - use part i (bc of 'hence'). in part i, you have one inequality wiht a^3 + b^3, and you made two more for b^3 + c^3 and c^3 + a^3. add those three together, then from there you will get the inequality
 

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