Halaman 36 - Matematika Latihan 1.3

3. Tentukan hasil dari

    a. 5 × ( 15 −6)

    b. 12 × (−7) + (−6) ÷ (−2)
    c. −15 ÷ (−3) −7 × (−4)
    d. [1 + 2 ÷ 3 × 4] × [9 × 7 (7 –8) ÷ (6 + 5)]

Jawab:

a. 5 × ( 15 −6) 
     Bentuk panjang:      5 × ( 15 −6) = 5 × 15 − 5 × 6
                                                                = 75   -  30
                                                                = 45

     Bentuk pendek:       5 × (15 − 6)  = 5  × (9)
                                                                = 45 

b. 12 × (−7) + (−6) ÷ (−2)
     
     12 × (−7) + (−6) ÷ (−2)  =  (12 × 7)    +  (-6/-2)
                                                 =      84         +   3
                                                 =      87

c. −15 ÷ (−3) − 7 × (−4)

     −15 ÷ (−3) − 7 × (−4)      = (−15/−3) − (7 × (−4))
                                                 =      5          −  ( -28 )                                                  =      5          +  28
                                                 =      33     

d. [1 + 2 ÷ 3 × 4] × [9 ×  7 (7 –8) ÷ (6 + 5)]                                                      

    = [1   + 2 × 4/3]     × [9 ×  7 × (-1)   :     11

     = [3/3 + 8/3]          × - 63                 :  11
     = [11/3]                     × - 63                 :  11
    =  -21

   Penjelasan 7 (7 - 8) sama artinya dengan  7 × (7 - 8)
   a. Penyelesaian bentuk panjang:
                         7 × (7 - 8) = (7 × 7)  -  (7 × 8)
                                            =    49      -    56
                                            = - 7
   b. Penyelesaian bentuk pendek, penjumlahan di dalam kurung diselesaikan dahulu.
                         7 × (7 - 8) = 7 × (7 - 8)
                                            =  7 × ( - 1 )
                                            = - 7