a) $\dfrac{SAMC}{SDMC}$ `=` $\dfrac{AM}{DC}$ `=3/5`

→ `SAMC = 3/5 × SDMC`

b) $\dfrac{SMBC}{SAMC}$ `=` $\dfrac{MB}{AM}$ `= 2/3`

→ `SMBC = 2/3 × SAMC = 2/3 × 27 =18` $cm^{2}$

$\dfrac{SADC}{SAMC}$ `=` $dfrac{AM}{DC}$ `= 3/5`

→ `SADC = 5/3 × SAMC = 5/3 × 27 = 45` $cm^{2}$

`SABCD = SMBC + SAMC + SADC = 18 + 27 + 45 = 90` $cm^{2}$

                                   Đáp số : a) `3/5`

                                                 b) `90` $cm^{2}$

` a, ` $\dfrac{SAMC}{SDMC}$ ` = ` $\dfrac{AM}{DC}$ ` = ` ` 3/5 `

$\rightarrow$ $\text{SAMC}$ ` = ` ` 3/5 ` ` × ` $\text{SDMC}$

` b, ` $\dfrac{SMBC}{SAMC}$ ` = ` $\dfrac{MB}{AM}$ ` = ` ` 2/3 `

$\rightarrow$ $\text{SMBC}$ ` = ` ` 2/3 ` ` × ` $\text{SAMC}$ ` = ` ` 2/3 ` ` × ` ` 27 ` ` = ` ` 18 ` $\text{cm²}$

$\dfrac{SADC}{SAMC}$ ` = ` $\dfrac{AM}{DC}$ ` = ` ` 3/5 `

$\rightarrow$ $\text{SADC}$ ` = ` ` 5/3 ` ` × ` $\text{SAMC}$ ` = ` ` 5/3 ` ` × ` ` 27 ` ` = ` ` 45 ` $\text{cm²}$

$\text{SABCD}$ ` = ` $\text{SMBC}$ ` + ` $\text{SAMC}$ ` + ` $\text{SADC}$ ` = ` ` 18 + 27 + 45 = 90 ` $\text{cm²}$
                                       $\text{Đáp số : a,}$ ` 3/5 `
                                                     $\text{b,}$ ` 90 ` $\text{cm²}$