One-dimensional linear equation: ax+b=c
Quadratic formula: x = (-b √ (b? -4ac))/2a
Square difference formula: (a+b)? =a？ +2ab+b？ , (A-B)? =a？ -2ab+b？
Formulas of trigonometric functions:
Sine theorem: a/sinA = b/sinB = c/sinC
Cosine theorem: a? =b？ +c？ -2bc cosA，b？ =a？ +c？ -2ac cosB，c？ =a？ +b？ -2ab cosC
Tangent theorem: tanA = sinA/cosA
Similar triangles formula: equal proportion theorem, angular bisector theorem, sine theorem, cosine theorem and tangent theorem.
Isosceles triangle formula: base angle theorem, equal angle theorem, isosceles triangle height formula.
Formula of circle: area formula of circle S=πr? , the circumferential formula l = 2π r.
Pythagorean Theorem: A? +b？ =c？
Trapezoidal formula: trapezoidal area formula S= (upper bottom+lower bottom) × height /2.
Series formulas: general formula, tolerance formula, first formula, last formula and number formula.
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The above formula is only a part of junior high school mathematics, and there are many other formulas. In the process of learning mathematics, we need to accumulate, understand and master the application of various formulas in order to better master mathematical knowledge.