//<![CDATA[ aax_getad_mpb({ "slot_uuid":"f485bc30-20f5-4c34-b261-5f2d6f6142cb" }); //]]> is it true that ||z| - |w|| \leq |z + w| ??

is it true that

[itex] ||z| - |w|| \leq |z + w| [/itex]??

if so what is the proof?

here is my workin so far.. please verify it thanks.

We know [itex] |z+w| \leq |z|+|w| [/itex]

let c = z - w, so [itex] |c+w| \leq |c|+|w| [/itex]

Now z = c + w,

so [itex] |z| \leq |c|+|w| [/itex]

[itex] |z| \leq |z-w| + |w| [/itex]

[itex] |z-w| \geq |z| -|w| [/itex]

Now let d = - w,

so [itex] |z - d| \geq |z| - |d| [/itex]

subbing in -w for d we get, [itex] |z + w| \geq |z| - |d| [/itex]

subbing in |w| for |d| since they are equal, we get [itex] |z + w| \geq ||z| - |w|| [/itex]

(i added an extra modulus bracket outside the right hand side at the end of the equation).

End of proof.

Is this correct please? please guide me if i am wrong?

**Physics Forums - The Fusion of Science and Community**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Is it true that ||z| - |w|| \leq |z + w| ?

Have something to add?

**Physics Forums - The Fusion of Science and Community**