Question 2
Find the values of for each of the following quadratic equations, so that they have two equal roots.
(i)
(ii)
- A standard quadratic equation is given by (where ).
- The nature of the roots is determined by the discriminant :
- For two equal real roots, the discriminant must be zero ().
- We determine coefficients and for each equation, substitute them into , and solve for .
- Remember: The coefficient of () must not be zero for the equation to remain quadratic.
(i)
Step 1 · Apply Discriminant Condition and Solve for
Comparing with :
For two equal roots, the discriminant must be zero ():
(i)
(ii)
Step 1 · Expand and Apply Discriminant Condition
Expanding the equation:
Comparing with :
For two equal roots, :
Step 2 · Solve for and Check Validity
From :
If , the original equation simplifies to , which is not a quadratic equation ().
Therefore, , leaving:
(ii)
- Missing Negative Root in (i): When solving , forgetting the sign gives only instead of both and .
- Retaining in (ii): Failing to reject . For to be a valid quadratic equation, the coefficient of cannot be zero ().
- Expansion Error in (ii): Forgetting to distribute to both terms inside the parentheses before identifying and .
More questions in Exercise 4.3
Find the nature of the roots of the following quadratic equations. If the real roots exist, find them:
(i)
(ii)
(iii)
Find the values of for each of the following quadratic equations, so that they have two equal roots.
(i)
(ii)
Is it possible to design a rectangular mango grove whose length is twice its breadth, and the area is ? If so, find its length and breadth.
Is the following situation possible? If so, determine their present ages.
The sum of the ages of two friends is years. Four years ago, the product of their ages in years was .
Is it possible to design a rectangular park of perimeter and area ? If so, find its length and breadth.