x 2 + y 2 + 5 x − 3 y + 4 = 0 x^{2}+y^{2}+5x-3y+4=0 x 2 + y 2 + 5 x − 3 y + 4 = 0
arg ( z + α z + β ) = π 4 , z = x + i y \arg\!\left(\dfrac{z+\alpha}{z+\beta}\right)=\dfrac{\pi}{4}, \qquad z=x+iy arg ( z + β z + α ) = 4 π , z = x + i y
Find α , β so that this locus = the given circle \text{Find } \alpha, \beta \text{ so that this locus } = \text{ the given circle} Find α , β so that this locus = the given circle
( 1 ) α = − 1 ( 2 ) α β = 4 ( 3 ) α β = − 4 ( 4 ) β = 4 (1)\ \alpha = -1 \quad (2)\ \alpha\beta = 4 \quad (3)\ \alpha\beta = -4 \quad (4)\ \beta = 4 ( 1 ) α = − 1 ( 2 ) α β = 4 ( 3 ) α β = − 4 ( 4 ) β = 4
x 2 + y 2 + 5 x − 3 y + 4 = 0 x^{2}+y^{2}+5x-3y+4=0 x 2 + y 2 + 5 x − 3 y + 4 = 0
( x + 5 2 ) 2 + ( y − 3 2 ) 2 = 9 2 \left(x+\dfrac{5}{2}\right)^{2}+\left(y-\dfrac{3}{2}\right)^{2}=\dfrac{9}{2} ( x + 2 5 ) 2 + ( y − 2 3 ) 2 = 2 9
Centre C ( − 5 2 , 3 2 ) , r = 3 2 \text{Centre } C\!\left(-\dfrac{5}{2},\dfrac{3}{2}\right),\quad r=\dfrac{3}{\sqrt{2}} Centre C ( − 2 5 , 2 3 ) , r = 2 3
arg ( z + α ) − arg ( z + β ) = π 4 \arg(z+\alpha)-\arg(z+\beta)=\dfrac{\pi}{4} arg ( z + α ) − arg ( z + β ) = 4 π
∠ at z subtended by ( − α , − β ) = π 4 \angle \text{ at } z \text{ subtended by } (-\alpha,-\beta) = \dfrac{\pi}{4} ∠ at z subtended by ( − α , − β ) = 4 π
z = − α ⇒ z + α = 0 ; z = − β ⇒ z + β = 0 z=-\alpha \Rightarrow z+\alpha=0;\qquad z=-\beta \Rightarrow z+\beta=0 z = − α ⇒ z + α = 0 ; z = − β ⇒ z + β = 0
So the circle passes through the real points − α , − β \text{So the circle passes through the real points } -\alpha,\ -\beta So the circle passes through the real points − α , − β
y = 0 : x 2 + 5 x + 4 = 0 ⇒ ( x + 1 ) ( x + 4 ) = 0 y=0:\ x^{2}+5x+4=0 \Rightarrow (x+1)(x+4)=0 y = 0 : x 2 + 5 x + 4 = 0 ⇒ ( x + 1 ) ( x + 4 ) = 0
x = − 1 , − 4 x=-1,\ -4 x = − 1 , − 4
{ − α , − β } = { − 1 , − 4 } ⇒ { α , β } = { 1 , 4 } \{-\alpha,-\beta\}=\{-1,-4\} \Rightarrow \{\alpha,\beta\}=\{1,4\} { − α , − β } = { − 1 , − 4 } ⇒ { α , β } = { 1 , 4 }
α β = 4 \alpha\beta = 4 α β = 4
On the arc: arg ( z + 1 ) > arg ( z + 4 ) \text{On the arc: } \arg(z+1) > \arg(z+4) On the arc: arg ( z + 1 ) > arg ( z + 4 )
⇒ α = 1 , β = 4 \Rightarrow \alpha = 1,\qquad \beta = 4 ⇒ α = 1 , β = 4
( 1 ) α = − 1 : × ; ( 2 ) α β = 4 : ✓ (1)\ \alpha=-1:\ \times;\qquad (2)\ \alpha\beta=4:\ \checkmark ( 1 ) α = − 1 : × ; ( 2 ) α β = 4 : ✓
( 3 ) α β = − 4 : × ; ( 4 ) β = 4 : ✓ (3)\ \alpha\beta=-4:\ \times;\qquad (4)\ \beta=4:\ \checkmark ( 3 ) α β = − 4 : × ; ( 4 ) β = 4 : ✓
Answer: (2) and (4) \boxed{\text{Answer: (2) and (4)}} Answer: (2) and (4)