Question:medium
If
\[
\begin{bmatrix}
a & c & 0 \\
b & d & 0 \\
0 & 0 & 5
\end{bmatrix}
\]
is a scalar matrix, then the value of
\[
a + 2b + 3c + 4d
\]
is:
If
\[
\begin{bmatrix}
a & c & 0 \\
b & d & 0 \\
0 & 0 & 5
\end{bmatrix}
\]
is a scalar matrix, then the value of
\[
a + 2b + 3c + 4d
\]
is:
Show Hint
In scalar matrices, diagonal elements are constant, and off-diagonal elements are zero.
Updated On: Feb 25, 2026
- \( 0 \)
- \( 5 \)
- \( 10 \)
- \( 25 \)
Show Solution
The Correct Option is D
Solution and Explanation
Step 1: Define scalar matrix
A scalar matrix is a diagonal matrix with identical diagonal elements. For instance, \( a = d = 5 \) and all off-diagonal elements (\( b \), \( c \)) are zero.
Step 2: Substitute values
Applying scalar matrix properties:\[a + 2b + 3c + 4d = 5 + 2(0) + 3(0) + 4(5) = 5 + 0 + 0 + 20 = 25.\]Step 3: Confirm solution
The calculated value is \( 25 \), matching option (D).
A scalar matrix is a diagonal matrix with identical diagonal elements. For instance, \( a = d = 5 \) and all off-diagonal elements (\( b \), \( c \)) are zero.
Step 2: Substitute values
Applying scalar matrix properties:\[a + 2b + 3c + 4d = 5 + 2(0) + 3(0) + 4(5) = 5 + 0 + 0 + 20 = 25.\]Step 3: Confirm solution
The calculated value is \( 25 \), matching option (D).
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