a) Hiệu số phần bằng nhau là:

5 - 3 = 2 (phần)

Độ dài đáy là:

28 : 2 x 5 = 70 (cm)

Chiều cao là:

28 : 2 x 3 = 42 (cm)

                Đ/S: độ dài đáy: 70 cm

                        chiều cao: 42 cm

b) Diện tích HBH là:

70 x 42 = 2940 (cm2)

                Đ/S: 2940 cm2

5-3=2

28:2x5=70

28:2x5=42

70x24=2940

Ta có sơ đồ:

Đáy          /........../........../........../........../........../

Chiều cao/........../........../........../     28 cm

a)Chiều cao của miếng bìa là:

28 : (5 - 3) x 3 = 42 (cm)

Độ dài đáy của miếng bìa là:

42 + 28 = 70 (cm)

b) Diện tích miếng bìa là:

42 x 70 = 2940 (cm2)

đúng ko đấy -  - 

                      -

Chiều cao miếng bìa là : 

   28 × 4/7 = 16 ( cm ) 

Diện tích miếng bìa là : 

   28 × 16 = 448 ( cm² ) 

     Đáp số : 448 cm² 

CHÚC BẠN HỌC GIỎI !!!

Chiều cao là:

28 : 7 x 4 = 16 (cm)

Diện tích miếng bìa là:

16 x 28 = 448 (cm²)

Đáp số : 448 cm²

Tk mk nha!

Hiệu tỉ số :

5 - 3 = 2

Độ dài đáy :

28 : 2 x 5 = 70 (cm)

Chiều cao :

70 - 28 = 42 (cm)

Diện tích :

\(70\times42=2940\left(cm^2\right)\)

.

a) Độ dài đáy hình bình hành là:

         28 : 2 x 5 = 70 ( cm )

    Chiều cao hình bình hành là:

          70 - 28 = 42 ( cm )

b) Diện tích miếng bìa hình bình hành là:

          70 x 42 = 2940 ( cm\(^2\))

               Đáp số: 2940  cm\(^2\)

mình làm có đúng ko z ??????????????????????????

Đổi 7 m 5 cm = 705 cm

độ dài đáy của hình bình hành là:

( 705+15) : 2=360 (cm )

Chiều cao của hình bình hành là:

705 -360= 345 (cm)

Diện tích hình bình hành là:

( 360 +345) x 2=1410( cm2)

           Đáp số: 1410 cm2

Độ dài đáy là : 52 + 12 = 64 ( cm )

                        Diện tích miếng bìa là :

                                64 x 52 = 3328 ( cm²)

                                       Đáp số : 3328 cm ² 

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