∣∣∣→a+→b∣∣∣2=∣∣→a∣∣2+∣∣∣→b∣∣∣2+2∣∣→a∣∣∣∣∣→b∣∣∣.cosθ
∣∣→a∣∣2+∣∣∣→b∣∣∣2=∣∣→a∣∣2+∣∣∣→b∣∣∣2+2∣∣→a∣∣+∣∣∣→b∣∣∣∵−1⩽cosθ⩽1
Rightarrow2∣∣→a∣∣∣∣∣→b∣∣∣cosθ⩽2∣∣→a∣∣∣∣∣→b∣∣∣
So,
∣∣∣→a+→b∣∣∣2⩽(∣∣→a∣∣∣∣∣→b∣∣∣)2
⇒∣∣∣→a+→b∣∣∣⩽∣∣→a∣∣+∣∣∣→b∣∣∣
Which is the required answer.
![1148354_1198284_ans_02a0c89b4fcb44a3aa04b92262407bab.png](https://search-static.byjusweb.com/question-images/toppr_invalid/questions/1148354_1198284_ans_02a0c89b4fcb44a3aa04b92262407bab.png)