3. Garis y = – 2x + c menyinggung lingkaran x2 + y2 – 2x – 2y – 15 = 0. Tent. Nilai c !

substitusi y = – 2x + c ke x² + y² – 2x – 2y – 15 = 0

x² + (–2x + c)² - 2x - 2(– 2x + c) - 15 = 0

5x² - 4xc + c² - 2x + 4x - 2c - 15 = 0

5x² + (2-4c)x + (c² - 2c - 15) = 0

agar menyinggung lingkaran, maka nilai
D = 0
b² - 4ac = 0
(2 - 4c)² - 4(5)(c² - 2c - 15) = 0
4 - 16c + 16c² - 20c² + 40c + 300 = 0
-4c² + 24c +304 = 0
4c² - 24c - 304 = 0
c² - 6c - 76 = 0
(c - )(c + ) = 0
jadi c = atau c =

Y=y
Jawabannya c=12
Saya sarankan download desmos