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 trapezoid area = (upper base+lower base) × height ÷2, S= 1/2(a+b)h circular area = radius × radius × π. /360
Linear function formulas Linear functions have the following expressions.
Point oblique type: y-b = k (x-a); The slope k and the intersection (a, b) are known.
Two-point formula: (y-b)/(x-a) = (b-d)/(a-c); It is known that the slopes of two points (a, b) and (c, d) are (b-d)/(a-c): y = kx+b; Given the slope k, the y-axis intercept is b, that is, the intersection point (0, b) is inclined according to the point.
Interception formula: x/a+y/b =1; It is known that the intercepts of X axis and Y axis are a and b respectively, that is, they pass through two points (a, 0) and (0, b) according to the two-point formula.
Quadratic function formula Quadratic function is a parabola, and there are three expressions.
General formula: y=ax? +bx+c； (a≠0)
Vertex: y=a(x-h)? +k； [a≠0 fixed point (h, k)]
Intersection point: y = a (x-x1) (x-x2); [The parabola intersects the X axis at (x 1, 0)(x2, 0)]
Quadratic function expression y=ax? +bx+c； Quadratic function is an axisymmetric figure.
Quadratic coefficient a determines the opening direction (a >；; 0, the opening is upward; A<0, opening down)
Symmetry axis: x = -b/2a
Vertex coordinates: [-b/2a, (4ac-b? )/4a ]
δ= b？ -4ac；
Number of intersections between parabola and X axis (δ >; 0, 2 intersections; When δ = 0, 1 intersection; δ& lt； 0, no intersection)
The formula of the sum of two angles of trigonometric function
sin(A+B)= Sina cosb+cosa sinb sin(A-B)= Sina cosb-sinb cosa
cos(A+B)= cosa cosb-Sina sinb cos(A-B)= cosa cosb+Sina sinb
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)
Double angle formula
tan2A = 2 tana/( 1-tan2A)ctg2A =(ctg2A- 1)/2c TGA
cos2a = cos2a-sin2a = 2 cos2a- 1 = 1-2 sin2a
half-angle formula
sin(A/2)=√(( 1-cosA)/2)sin(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))
The above are all the formulas I summarized for junior high school mathematics, which are for reference only and I hope to help you.