Soal
1. 
2. 
3. 
4. 
5. 
Penyelesaian
1. y = x^2 – 25
y = 0
0 = x^2 – 25
(x – 5) (x + 5 )
x = 5 x = -5
(5, 0) (-5, 0)
x = 0
y = 0^2 – 25
y = -25
(0, -25)
Xp = - (b/2a)
= -(0/2.1)
= 0
Yp = -(b^2 – 4ac/4a)
= -(0^2 – 4.1.-25/4.1)
= -(0+100/4)
= -25
(0, -25)
2. y = -x^2 + 7x – 12
y = 0
0 = x^2 + 7x – 12
(-x + 4 ) (x – 3)
x = 4 x = 3
(4, 0) (3, 0)
x = 0
y = 0^2 +7(0) – 12
y = -12
(0, -12)
Xp = -(b/2a)
= -(7/2.-1)
= -(7/-2)
= 3,5
Yp =-(b^2 – 4ac/4a)
= -(7^2 – 4.-1.-12/4.-1)
= -(49 – 48/-4)
= -(1/-4)
= 0,25
(3,5; 0,25)
3. y = –x^2 – 8x + 9
y = 0
0 = -x^2 – 8x + 9
(-x – 9) (x – 1)
x = -9 x = 1
(-9, 0) (1, 0)
x = 0
y = -0^2 -8(0) + 9
y = 9
(0, 9)
Xp = -(b/2a)
= -(-8/2.(-1))
= -4
Yp = -(b^2 – 4ac/4a)
= -(-8^2 – 4(-1).9)/4(-1))
= -(64 + 36/-4)
= - (-25)
= 25
(-4, 25)
4.
y = 0
(0,5; 0) (-4, 0)
x = 0
y = -2.0^2 – 7.0 + 4
y = 4
Xp = -(b/2a)
= -(-7/2.-2)
=-(-7/-4)
= - 1,75
Yp = -(b^2 – 4ac/4a)
=- (7^2 – 4.-2.4/4.-2)
= -(49 + 32/-8)
= -(-10,125)
= 10,125
(-1,75; 10,125)
5. y = -x^2 + 6x
y = 0
-x^2 + 6x
x(-x + 6) = 0
x = 0 x = 6
(0, 0) (6,0)
x = 0
y = 0^2 + 6(0)
y = 0
(0, 0)
Xp = -(b/2a)
= -(6/2.-1)
= -(-3)
= 3
Yp = -(b^2 – 4ac/4a)
= -(6^2 – 4.-1.0/4(-1))
= -(36 – 0/-4)
= -(-9)
= 9
(3, 9)
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