This question was asked inGPSC Deputy Executive Engineer (Electrical) Paper 2024Question 29 of 33 published · Gujarat Public Service CommissionOpen paper
Q128ModerateSystem Properties

Out of the following systems with input x(t) and output y(t), identify the linear system.

Answer & step-by-step solution
Correct answer: B. dy/dt + 2t y(t) = t²x(t)
Quick explanation

A system is linear when input, output and output derivatives appear only to the first power and are not multiplied together; coefficients may still depend on time. In option B, dy/dt+2t y=t²x satisfies this condition. The other listed equations contain squared signal terms. Therefore option B is linear.

Linear form: a1(t)dy/dt+a0(t)y=b0(t)x

Concept and Reasoning

A system is linear when input, output and output derivatives appear only to the first power and are not multiplied together; coefficients may still depend on time. In option B, dy/dt+2t y=t²x satisfies this condition. The other listed equations contain squared signal terms. Therefore option B is linear.

Calculation / Key Relation

Linear form: a1(t)dy/dt+a0(t)y=b0(t)x

Exam Takeaway

Time-varying coefficients do not make a system nonlinear.

Common Mistake

Look for powers/products of x, y or derivatives, not merely the presence of t-dependent coefficients.

Quick Trick

Time-varying coefficients do not make a system nonlinear.

Solution diagram – Out of the following systems with input x(t) and output y(t), identify the…
Exam tipTime-varying coefficients do not make a system nonlinear.
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