Which of the following quadratic equations has real roots?
- A4x
2
−7x+5=0 - B5x
2
−11x+7=0 - C5x
2
−11x+8=0 - D2x
2
−7x+5=0
Solution & Step-by-step Explanation
A quadratic equation ax
2
+bx+c=0 has real roots if its discriminant (D) is greater than or equal to zero (D≥0), where:
D=b
2
−4ac
Let's check the options one by one:
Option A: 4x
2
−7x+5=0
a=4,b=−7,c=5
D=(−7)
2
−4(4)(5)=49−80=−31<0 (Roots are imaginary)
Option B: 5x
2
−11x+7=0
a=5,b=−11,c=7
D=(−11)
2
−4(5)(7)=121−140=−19<0 (Roots are imaginary)
Option C: 5x
2
−11x+8=0
a=5,b=−11,c=8
D=(−11)
2
−4(5)(8)=121−160=−39<0 (Roots are imaginary)
Option D: 2x
2
−7x+5=0
a=2,b=−7,c=5
D=(−7)
2
−4(2)(5)=49−40=9>0 (Roots are real and distinct)
Therefore, the equation in option D has real roots.
2
+bx+c=0 has real roots if its discriminant (D) is greater than or equal to zero (D≥0), where:
D=b
2
−4ac
Let's check the options one by one:
Option A: 4x
2
−7x+5=0
a=4,b=−7,c=5
D=(−7)
2
−4(4)(5)=49−80=−31<0 (Roots are imaginary)
Option B: 5x
2
−11x+7=0
a=5,b=−11,c=7
D=(−11)
2
−4(5)(7)=121−140=−19<0 (Roots are imaginary)
Option C: 5x
2
−11x+8=0
a=5,b=−11,c=8
D=(−11)
2
−4(5)(8)=121−160=−39<0 (Roots are imaginary)
Option D: 2x
2
−7x+5=0
a=2,b=−7,c=5
D=(−7)
2
−4(2)(5)=49−40=9>0 (Roots are real and distinct)
Therefore, the equation in option D has real roots.