题霸题霸学习平台
← 返回公开题库
八年级数学解答题一般
题目
如图,ABC\triangle ABC的外角ACD\angle ACD的平分线CPCP与内角ABC\angle ABC平分线BPBP交于点PP,若BPC=40\angle BPC=40^{\circ},则CAP=\angle CAP=____.
知识点:三角形的三边关系、三角形的稳定性、三角形的外角性质、多边形内角与外角章节:第一章 三角形 / 1.1 认识三角形

答案与解析

答案

延长BABA,作PNBDPN\bot BDPFBAPF\bot BAPMACPM\bot AC

PCD=x\angle PCD=x^{\circ}

CP\because CP平分ACD\angle ACD

ACP=PCD=x\therefore \angle ACP=\angle PCD=x^{\circ}PM=PNPM=PN

BP\because BP平分ABC\angle ABC

ABP=PBC\therefore \angle ABP=\angle PBCPF=PNPF=PN

PF=PM\therefore PF=PM

BPC=40\because \angle BPC=40^{\circ}

ABP=PBC=PCDBPC=(x40)\therefore \angle ABP=\angle PBC=\angle PCD-\angle BPC=\left(x-40\right)^{\circ}

BAC=ACDABC=2x(x40)(x40)=80\therefore \angle BAC=\angle ACD-\angle ABC=2x^{\circ}-\left(x^{\circ}-40^{\circ}\right)-\left(x^{\circ}-40^{\circ}\right)=80^{\circ}

CAF=100\therefore \angle CAF=100^{\circ}

RtPFARt\triangle PFARtPMARt\triangle PMA中,

{PA=PAPM=PF\because \left\{\begin{array}{}PA=PA \\ PM=PF\end{array}\right.

RtPFA\therefore Rt\triangle PFARtPMA(HL)Rt\triangle PMA\left(HL\right)

FAP=PAC=50\therefore \angle FAP=\angle PAC=50^{\circ}.

故答案为:5050^{\circ}.

解析

延长BABA,作PNBDPN\bot BDPFBAPF\bot BAPMACPM\bot AC

PCD=x\angle PCD=x^{\circ}

CP\because CP平分ACD\angle ACD

ACP=PCD=x\therefore \angle ACP=\angle PCD=x^{\circ}PM=PNPM=PN

BP\because BP平分ABC\angle ABC

ABP=PBC\therefore \angle ABP=\angle PBCPF=PNPF=PN

PF=PM\therefore PF=PM

BPC=40\because \angle BPC=40^{\circ}

ABP=PBC=PCDBPC=(x40)\therefore \angle ABP=\angle PBC=\angle PCD-\angle BPC=\left(x-40\right)^{\circ}

BAC=ACDABC=2x(x40)(x40)=80\therefore \angle BAC=\angle ACD-\angle ABC=2x^{\circ}-\left(x^{\circ}-40^{\circ}\right)-\left(x^{\circ}-40^{\circ}\right)=80^{\circ}

CAF=100\therefore \angle CAF=100^{\circ}

RtPFARt\triangle PFARtPMARt\triangle PMA中,

{PA=PAPM=PF\because \left\{\begin{array}{}PA=PA \\ PM=PF\end{array}\right.

RtPFA\therefore Rt\triangle PFARtPMA(HL)Rt\triangle PMA\left(HL\right)

FAP=PAC=50\therefore \angle FAP=\angle PAC=50^{\circ}.

故答案为:5050^{\circ}.

自由组卷

围绕这道题再组一份练习 →

完整试卷

浏览同年级试卷结构 →