Question

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Answer 1

Explanation:

use parallelogram law of vector

$r = \sqrt{ {a}^{2} + {b}^{2} + 2ab \cos( \alpha ) }$

$r = \sqrt{ {120}^{2} + {40}^{2} + 2 \times 120 \times 40 \cos( \alpha ) }$

cos =60 Degree for (1)

$r = \sqrt{ {120}^{2} + {40}^{2} + 2 \times 40 \times 120 \cos(60) }$

solve this u get urs answer perfectly