KCET · Maths · Quadratic Equation

If \( \vec{a}=\hat{i}+2 \hat{j}+2 \hat{k},|\vec{b}|=5 \) and the angle between \( \vec{a} \) and \( \vec{b} \) is \( \frac{\pi}{6} \), then the area of the
triangle formed by these two vectors as two sides is

A \( \frac{15}{2} \)
B \( 15 \)
C \( \frac{15}{4} \)
D \( \frac{15 \sqrt{3}}{2} \)

Verified Solution

Answer & Solution

Correct Answer

(C) \( \frac{15}{4} \)

Step-by-step Solution

Detailed explanation

Given that \(\vec{a}=\hat{i}+2 \hat{j}+2 \hat{k} \rightarrow(1)\)
So, \(|\vec{a}|=\sqrt{1+4+4}=\sqrt{9}=3\)
\(|\vec{b}|=5\)
and angle between \(\vec{a}\) and \(\vec{b}\) is \(\frac{\pi}{6}\)
We know that area formed by two vectors as two sides is given by
Area \(=\frac{1}{2}|\vec{a}| \vec{b} \mid \sin \theta\)
\(=\frac{1}{2}(3)(5) \sin \frac{\pi}{6}=\frac{15}{4}\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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If \( \vec{a}=\hat{i}+2 \hat{j}+2 \hat{k},|\vec{b}|=5 \) and the angle between \( \vec{a} \) and \( \vec{b} \) is \( \frac{\pi}{6} \), then the area of thetriangle formed by these two vectors as two sides is

Step-by-step Solution

If \( \vec{a}=\hat{i}+2 \hat{j}+2 \hat{k},|\vec{b}|=5 \) and the angle between \( \vec{a} \) and \( \vec{b} \) is \( \frac{\pi}{6} \), then the area of the
triangle formed by these two vectors as two sides is