Discriminant b2-4ac=0. Note: The equation has two equal real roots.
B2-4ac >0, note that the equation has two unequal real roots.
B2-4ac & lt； 0, note that the equation has no real root, but a complex number of * * * yoke.
Perimeter formula junior high school perimeter formula is common in the following categories:
Rectangular perimeter = (length+width) ×2, C=2(a+b)
Square perimeter = side length ×4, C=4a
Circumference = diameter × π, C=2πr
Area formula The geometric area formula in junior high school is common in the following categories:
Rectangular area = length × width, S=ab
Square area = side length × side length, S=a?
Triangle area = base × height ÷2, S=ah/2.
Parallelogram area = base × height, S=ah
Trapezoidal area = (upper bottom+lower bottom) × height ÷2, s =1/2 (a+b) h.
Formulas of trigonometric functions 1, two-angle sum formula
sin(A+B)=sinAcosB+cosAsinB，sin(A-B)=sinAcosB-sinBcosA
cos(A+B)=cosAcosB-sinAsinB，cos(A-B)=cosAcosB+sinAsinB
tan(A+B)=(tanA+tanB)/( 1-tanA tanB)，tan(A-B)=(tanA-tanB)/( 1+tanA tanB)
ctg(A+B)=(ctgActgB- 1)/(ctg B+ctgA)，ctg(A-B)=(ctgActgB+ 1)/(ctg B-ctgA)
2. Double angle formula
tan2A=2tanA/( 1-tan2A)，ctg2A=(ctg2A- 1)/2ctga
cos2a = cos2a-sin2a = 2 cos2a- 1 = 1-2 sin2a
3. Half-angle formula
sin(A/2)=√(( 1-cosA)/2)，ain(A/2)=-√(( 1-cosA)/2)
cos(A/2)=√(( 1+cosA)/2)，cos(A/2)=-√(( 1+cosA)/2)
tan(A/2)=√(( 1-cosA)/(( 1+cosA))，tan(A/2)=-√(( 1-cosA)/(( 1+cosA))
ctg(A/2)=√(( 1+cosA)/(( 1-cosA))，ctg(A/2)=-√(( 1+cosA)/(( 1-cosA))
4. Sum-difference product
2sinAcosB=sin(A+B)+sin(A-B)，2cosAsinB=sin(A+B)-sin(A-B)
2cosAcosB=cos(A+B)-sin(A-B)，-2sinAsinB=cos(A+B)-cos(A-B)
sinA+sinB = 2 sin((A+B)/2)cos((A-B)/2，cosA+cosB = 2 cos((A+B)/2)sin((A-B)/2)
tanA+tanB=sin(A+B)/cosAcosB，tanA-tanB=sin(A-B)/cosAcosB
ctgA+ctgBsin(A+B)/sinAsinB，-ctgA+ctgBsin(A+B)/sinAsinB
The above is my junior high school math formula, I hope I can help you.