Tolong kerjakan nomor 20 dan 21 . Mohon bantuannya dan buat caranya

20)
(-1/2,0)
y= ax^-5x-3
memotong sumbu x (y=0)
y= ax^-5x-3
0= a(-1/2)^-5(-1/2)-3
0= 1/4a+5/2-3
3-5/2= 1/4a
6/2-5/2= 1/4a
1/2= 1/4a
1/2:1/4= a
1/2×4/1= a
2= a

21)
f(x)= -x^+2x+3
X= -b/2a= -2/2.(-1)= -2/-2= 1
Y= D/ -4a= b^-4ac/-4a= 2^-4.(-1).3/-4.(-1)= 4+12/4= 16/4= 4
jawabannya (1,4)