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Question 1: Which of the following is NOT a quadratic equation?
Solution: (B) $x(x+1) + 8 = (x+2)(x-2)$
Step 1: Simplify LHS: $x^2 + x + 8$.
Step 2: Simplify RHS: $x^2 - 4$.
Step 3: $x^2 + x + 8 = x^2 - 4 \Rightarrow x + 12 = 0$. This is a linear equation. -
Question 2: The roots of the quadratic equation $x^2 - 0.04 = 0$ are:
Solution: (A) $\pm 0.2$
Step 1: $x^2 = 0.04$.
Step 2: $x = \sqrt{0.04} = \pm 0.2$. -
Question 3: The discriminant of the quadratic equation $2x^2 - 4x + 3 = 0$ is:
Solution: (A) -8
Step 1: $D = b^2 - 4ac$. Here $a=2, b=-4, c=3$.
Step 2: $D = (-4)^2 - 4(2)(3) = 16 - 24 = -8$. -
Question 4: If the equation $x^2 + 4x + k = 0$ has real and distinct roots, then:
Solution: (A) $k < 4$
Step 1: For real and distinct roots, $D > 0$.
Step 2: $b^2 - 4ac > 0 \Rightarrow 4^2 - 4(1)(k) > 0$.
Step 3: $16 - 4k > 0 \Rightarrow 16 > 4k \Rightarrow k < 4$. -
Question 5: The nature of roots of the equation $2x^2 - \sqrt{5}x + 1 = 0$ is:
Solution: (C) No real roots
Step 1: Calculate $D = b^2 - 4ac$.
Step 2: $D = (-\sqrt{5})^2 - 4(2)(1) = 5 - 8 = -3$.
Step 3: Since $D < 0$, the equation has no real roots. -
Question 6: If one root of the equation $2x^2 + kx - 6 = 0$ is 2, then the value of $k$ is:
Solution: (B) -1
Step 1: Substitute $x=2$ in the equation.
Step 2: $2(2)^2 + k(2) - 6 = 0 \Rightarrow 8 + 2k - 6 = 0$.
Step 3: $2k + 2 = 0 \Rightarrow 2k = -2 \Rightarrow k = -1$. -
Question 7: The sum of the roots of the quadratic equation $3x^2 - 9x + 5 = 0$ is:
Solution: (A) 3
Step 1: Sum of roots $= -b/a$.
Step 2: Here $a=3, b=-9$.
Step 3: Sum $= -(-9)/3 = 9/3 = 3$. -
Question 8: Which of the following equations has 2 as a root?
Solution: (C) $2x^2 - 7x + 6 = 0$
Step 1: Substitute $x=2$ in option (C).
Step 2: $2(2)^2 - 7(2) + 6 = 8 - 14 + 6 = 14 - 14 = 0$.
Step 3: Since LHS = RHS, 2 is a root. -
Question 9: If the roots of $ax^2 + bx + c = 0$ are equal, then $c$ is equal to:
Solution: (D) $b^2/4a$
Step 1: For equal roots, $D = 0 \Rightarrow b^2 - 4ac = 0$.
Step 2: $b^2 = 4ac$.
Step 3: $c = b^2 / 4a$. -
Question 10: Values of $k$ for which the quadratic equation $2x^2 - kx + k = 0$ has equal roots is:
Solution: (D) 0, 8
Step 1: For equal roots, $D = 0 \Rightarrow b^2 - 4ac = 0$.
Step 2: $(-k)^2 - 4(2)(k) = 0 \Rightarrow k^2 - 8k = 0$.
Step 3: $k(k-8) = 0 \Rightarrow k = 0$ or $k = 8$.