Question

who introduced zero group​

Answer 1

William Ramsay

Zero group elements or the noble gases were discovered and introduced by William Ramsay in 1902.

Answer 2

Answer:

The length, area and the perimeter of the rectangle are 21cm, 420 cm² and 82 cm respectively.

Step-by-step explanation:

Let the rectangle be ABCD.

According to the question :

➟ Diagonal : BD = 29cm

➟ Breadth : CD = 20cm

All the angles in a rectangle are 90°.

So, ∆BDC is a right angled triangle with ∠BCD = 90°. Using pythagoras theorem :

➟ (P)² + (B)² = (H)²

➟ (BC)² + (20)² = (29)²

➟ BC² + 400 = 841

➟ BC² = 841 – 400

➟ BC² = 441

➟ BC = √441

➟ BC = 21cm

∴ The length of the rectangle BC is 21 cm.

Now, let's find the area of the rectangle :

➟ Area of rectangle = Length × breadth

➟ A = 21cm × 20cm

➟ Area = 420cm²

∴ The area of the rectangle is 420 cm².

Finally, finding the perimeter of the rectangle :

➟ Perimeter = 2 (l + b)

➟ P = 2 (21cm + 20cm)

➟ P = 2 (41cm)

➟ Perimeter = 82cm

∴ The perimeter of the rectangle is 82 cm.

Explanation:

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