Answer to Question #157324 in Calculus for Janhavi

Question #157324

Prove that |x+y+z|<=|x|+|y|+|z|


1
Expert's answer
2021-01-25T03:03:21-0500

let a,bR\text {let }a,b\in{R}

ababa*b \le|a|*|b|

(a+b)2=a2+b2+2aba2+b2+2ab(a+b)^2=a^2+b^2+2a*b\le{a^2+b^2+2|a|*|b|}

a2+b2+2ab=a2+b2+2ab=(a+b)2a^2+b^2+2|a|*|b|=|a|^2+|b|^2+2|a|*|b|=(|a|+|b|)^2

(a+b)2(a+b)2(a+b)^2\le(|a|+|b|)^2

(a+b)2(a+b)2\sqrt{(a+b)^2}\le\sqrt{(|a|+|b|)^2}

a+ba+b (1)|a+b|\le|a|+|b|\ (1)

x+y+z let a=x+y;b=z|x+y+z| \text{ let }a=x+y;b=z

from inequality (1)\text{from inequality }(1)

x+y+zx+y+zx+y+z|x+y+z|\le|x+y|+|z|\le|x|+|y|+|z|

proved.






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