Ecuatia de gradul doi, cand se cunosc solutiile, arata asa : x²-Sx+P=0, unde S=x₁+x₂ si P=x₁x₂
a)S=4, P=3 =>x²-4x+3=0
b)S=1, P=-20 =>x²-x-20=0
c)S=-3, P=2 =>x²+3x+2=0
d)S=5/4, P=3/8 =>x² - 5/4x + 3/8 = 0 sau 8x²-10x+3=0
e)S=0, P=-9 =>x²-9=0
f)S=6, P=8,75 =>x²-6x+875/100=0 sau x²-6x+35/4=0 sau 4x²-24x+35=0
g)S=4, P=1 =>x²-4x+1=0
h)S=-2, P=-1 =>x²+2x-1=0