Question

Giúp với ạ.

Answer 1

Bài 12:

CN+BN=CB

=>\(CN=CB-BN=CB-\frac13BC=\frac23BC\)

=>\(S_{CAN}=\frac23\times S_{CAB}=\frac23\times180=120\left(\operatorname{cm}^2\right)\)

Ta có: CM+MA=CA

=>\(CM=CA-AM=\frac12CA\)

=>\(S_{CMN}=\frac12\times S_{CNA}=\frac12\times120=60\left(\operatorname{cm}^2\right)\)

Bài 11:

\(AN=\frac13\times AB\)

=>\(AB=3\times AN\)

=>\(S_{ABM}=3\times S_{ANM}=3\times10=30\left(\operatorname{cm}^2\right)\)

\(AM=\frac14\times AC\)

=>\(AC=4\times AM\)

=>\(S_{ABC}=4\times S_{ABM}=4\times30=120\left(\operatorname{cm}^2\right)\)