Home/Differential Calculus/Tangent and normal lines/Formula4.2. Tangent and normal linesFormulaIn 4.2. Tangent and normal linesFormulaCopy LaTeXy−f(a)=f′(a)(x−a)y-f(a)=f'(a)(x-a)y−f(a)=f′(a)(x−a)TagsDifferential calculusDerivativeTangent and normal linesDerivative formulaDetailTangent line to y=f(x)y=f(x)y=f(x) at x=ax=ax=a.Explore the ideaExplore the ideaVariablesxxxIndependent variableaaaPoint or real constantfffFunctionf′f'f′Derivative of fffyyyDependent variableFound an error? Contact us.Related formulasRelatedFormulaf′(x)=limh→0f(x+h)−f(x)hf'(x)=\lim_{h\to0}\frac{f(x+h)-f(x)}{h}f′(x)=h→0limhf(x+h)−f(x)Open formulaOpen in sectionRelatedFormulay−f(a)=−1f′(a)(x−a),f′(a)≠0y-f(a)=-\frac{1}{f'(a)}(x-a),\qquad f'(a)\neq0y−f(a)=−f′(a)1(x−a),f′(a)=0Open formulaOpen in sectionRelatedFormulaf′(a)=limx→af(x)−f(a)x−af'(a)=\lim_{x\to a}\frac{f(x)-f(a)}{x-a}f′(a)=x→alimx−af(x)−f(a)Open formulaOpen in sectionRelatedFormulamtan=f′(a)m_{\mathrm{tan}}=f'(a)mtan=f′(a)Open formulaOpen in section