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If a⃗=2i^+mj^−nk^\vec{a} = 2\hat{i} + m\hat{j} - n\hat{k} and b⃗=li^−3j^+4k^\vec{b} = l\hat{i} - 3\hat{j} + 4\hat{k} such that a⃗=2b⃗\vec{a} = 2\vec{b} then the value of 14l+m+n14{l} + m + n is:

Solution

✅ Correct Option: 1

Given that a⃗=2b⃗\vec{a} = 2\vec{b}:

2i^+mj^−nk^=2(li^−3j^+4k^)2\hat{i} + m\hat{j} - n\hat{k} = 2(l\hat{i} - 3\hat{j} + 4\hat{k})

2i^+mj^−nk^=2li^−6j^+8k^2\hat{i} + m\hat{j} - n\hat{k} = 2l\hat{i} - 6\hat{j} + 8\hat{k}

Comparing the coefficients of i^,j^,\hat{i}, \hat{j}, and k^\hat{k}:

  • i^\hat{i}: 2=2l  ⟹  l=12 = 2l \implies l = 1
  • j^\hat{j}: m=−6m = -6
  • k^\hat{k}: −n=8  ⟹  n=−8-n = 8 \implies n = -8

Substitute these values into the required expression:

14l+m+n=14(1)+(−6)+(−8)=14−14=014l + m + n = 14(1) + (-6) + (-8) = 14 - 14 = 0

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