The 2nd relationship <u>|| u + v || = √ { || u ||² + || v ||² }</u>, and the 4th relationship <u>|| u + v || < || u || + || v ||</u> holds for the sum of the magnitudes of vectors u and v, which are perpendicular.
In the question, we are asked to identify the relationships that hold for the sum of the magnitudes of vectors u and v, which are perpendicular to each other.
The magnitude of a vector A is shown as || A ||.
Thus, the magnitude of vector u is || u ||, and of vector, v is || v ||.
By vector algebra, we know that,
|| u + v || = √ { || u ||² + || v ||² + 2( || u || )( || v || ) cos θ }, where θ is the angle between vector u and vector v.
Now, we are given that vectors u and v are perpendicular to each other, thus, θ = 90°, which gives cos θ = 0, or,
|| u + v || = √ { || u ||² + || v ||² }, making the 2nd relation true.
Now, we have, || u + v || = √ { || u ||² + || v ||² }.
Squaring both sides, we get:
|| u + v || ² = || u ||² + || v ||² = { || u || + || v || }² - 2(|| u ||)(|| v ||),
or, || u + v || ² < { || u || + || v || }² {Since, 2(|| u ||)(|| v ||) > 0},
or, || u + v || < || u || + || v || {Taking square roots}, making the 4th relation true.
Thus, the 2nd relationship <u>|| u + v || = √ { || u ||² + || v ||² }</u>, and the 4th relationship <u>|| u + v || < || u || + || v ||</u> holds for the sum of the magnitudes of vectors u and v, which are perpendicular.
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For the complete question, refer to the attachment.