Question -
Answer -
Given: 21x2 +9x + 1 = 0
We shall applydiscriminant rule,
Where, x = (-b ±√(b2 – 4ac))/2a
Here, a = 21, b = 9, c= 1
So,
x = (-9 ±√(92 – 4(21)(1)))/ 2(21)
= (-9 ± √(81-84))/42
= (-9 ± √(-3))/42
= (-9 ± √3(-1))/42
We have i2 =–1
By substituting –1 = i2 inthe above equation, we get
x = (-9 ± √3i2)/42
= (-9 ± √(√3i)2/42
= (-9 ± √3i)/42
= -9/42 ± √3i/42
= -3/14 ± √3i/42
∴ The roots of thegiven equation are -3/14 ± √3i/42