In each of these questions, two equations (I) and (II) are given. You have to solve both the equations and give answer.
1.
I. [latex]x^{5}[/latex] – 41[latex]x^{3}[/latex] + 400x = 0
II. [latex]y^{2}[/latex] – 14y + 30 = −18
A. if x ≥ y
B. if x ≤ y
C. if x ≥ y
D. if x ≤ y
E. if x = y or relationship between x and y can't be established
Answer: Option B
Explanation:
I. [latex]x^{5}[/latex] – 41[latex]x^{3}[/latex] + 400x = 0
x([latex]x^{4}[/latex] – 41[latex]x^{2}[/latex] + 400) = 0
x = 0 or [latex]x^{4}[/latex] – 41[latex]x^{2}[/latex] + 400 = 0
Let [latex]x^{2}[/latex] = a
[latex]a^{2}[/latex] – 41a + 400 = 0 ∴ [latex]a^{2}[/latex] – 25a − 16a + 400 = 0
(a – 16)(a – 25) = 0
a = 16 or a = 25
[latex]x^{2}[/latex] = 16 or [latex]x^{2}[/latex] = 25
x = ±4 or x = ±5
x = −5 or −4 or 0 or 4 or 5
II. [latex]y^{2}[/latex] – 14y + 30 = −18
[latex]y^{2}[/latex] – 14y + 48 = 0
[latex]y^{2}[/latex] – 8y − 6y + 48 = 0
(y – 6)(y – 8) = 0
y = 6 or y = 8
For both values of y
2.
I. [latex]x^{2}[/latex] – 3 = 2x
II. [latex]y^{2}[/latex] + 5y + 6 = 0
A. if x ≥ y
B. if x ≤ y
C. if x ≥ y
D. if x ≤ y
E. if x = y or relationship between x and y can't be established
Answer: Option B
Explanation:
I. [latex]x^{2}[/latex] – 3 = 2x
[latex]x^{2}[/latex] – 2x – 3 = 0
[latex]x^{2}[/latex] – 3x + x – 3 = 0
(x + 1)(x – 3) = 0
x = 3 or x = −1
II. [latex]y^{2}[/latex] + 5y + 6 = 0
[latex]y^{2}[/latex] + 3y + 2y + 6 = 0
(y + 3)(y + 2) = 0
y = –3 or y = –2
For both values of x, x ≥ y
3.
I. 4[latex]x^{3}[/latex] + 24[latex]x^{2}[/latex] – 64x = 0
II. 3[latex]y^{2}[/latex] + 39y + 126 = 0
A. if x ≥ y
B. if x ≤ y
C. if x ≥ y
D. if x ≤ y
E. if x = y or relationship between x and y can't be established
Answer: Option E
Explanation:
I. 4[latex]x^{3}[/latex] + 24[latex]x^{2}[/latex] – 64x = 0
4x([latex]x^{2}[/latex] + 6x – 16) = 0
4x = 0 or [latex]x^{2}[/latex] + 6x – 16 = 0 (Here 4x = 0 is nothing but x = 0)
[latex]x^{2}[/latex] + 6x – 16 = 0
[latex]x^{2}[/latex] + 8x − 2x – 16 = 0
(x − 2)(x + 8) = 0
x = 2 or x = −8
x = −8, 0 or 2
II. 3[latex]y^{2}[/latex] + 39y + 126 = 0
[latex]y^{2}[/latex] + 13y + 42 = 0
[latex]y^{2}[/latex] + 7y + 6y + 42 = 0
(y + 7)(y + 6) = 0
y = –7 or y = –6 When x = −8, x y Hence, no relation can be established between x and y.
4.
I. [latex]x^{2}[/latex] – 25x + 114 = 0
II. [latex]y^{2}[/latex] – 10y + 24 = 0
A. if x ≥ y
B. if x ≤ y
C. if x ≥ y
D. if x ≤ y
E. if x = y or relationship between x and y can't be established
Answer: Option C
Explanation:
I. [latex]x^{2}[/latex] – 25x + 114 = 0
[latex]x^{2}[/latex] – 19x – 6x + 114 = 0
(x – 6)(x – 19) = 0
x = 19 or x = 6
II. [latex]y^{2}[/latex] – 10y + 24 = 0
[latex]y^{2}[/latex] – 6y – 4y + 24 = 0
(y – 4)(y – 6) = 0
y = 6 or y = 4
When x = 19, x ≥ y
When x = 6, x ≥ y
Hence, x ≥ y
5.
I. 48[latex]x^{2}[/latex] – 24x + 3 = 0
II. 55[latex]y^{2}[/latex] + 53y + 12 = 0
A. if x ≥ y
B. if x ≤ y
C. if x ≥ y
D. if x ≤ y
E. if x = y or relationship between x and y can't be established
Answer: Option A
Explanation:
48[latex]x^{2}[/latex] – 24x + 3 = 0 is of the form a[latex]x^{2}[/latex] – bx + c = 0
Both roots of this equation are positive i.e. x ≥ 0
55[latex]y^{2}[/latex] + 53y + 12 = 0 is of the form a[latex]y^{2}[/latex] + by + c = 0
Both roots of this equation are negative i.e. y