JEE MAIN - Mathematics (2021 - 20th July Evening Shift - No. 14)
In a triangle ABC, if $$\left| {\overrightarrow {BC} } \right| = 3$$, $$\left| {\overrightarrow {CA} } \right| = 5$$ and $$\left| {\overrightarrow {BA} } \right| = 7$$, then the projection of the vector $$\overrightarrow {BA} $$ on $$\overrightarrow {BC} $$ is equal to :
$${{19} \over 2}$$
$${{13} \over 2}$$
$${{11} \over 2}$$
$${{15} \over 2}$$
Explanation
_20th_July_Evening_Shift_en_14_1.png)
Projection of $$\overrightarrow {BA} $$
on $${\overrightarrow {BC} }$$ is equal to
$$ = \left| {\overrightarrow {BA} } \right|\cos \angle ABC$$
$$ = 7\left| {{{{7^2} + {3^2} - {5^2}} \over {2 \times 7 \times 3}}} \right| = {{11} \over 2}$$
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