Explanation

The invention and advancement of the vacuum or electron tube marked the beginning of the Electronic Era in the early 20th century.

These tubes were used in early radios, televisions, and computers.

Explanation

The fundus is the upper, dome-shaped portion of the stomach above the esophageal opening.

It stores undigested food and gases released during digestion.

Explanation

The trigonometric identity is:

Sec²θ - Tan²θ = 1

Explanation

15 divided by -3:

15 ÷ (-3) = -5

Explanation

Metallic oxides react with water to form bases, as shown in the example:

Na₂O + H₂O → 2NaOH

This reaction demonstrates the basic nature of metallic oxides, forming a strong base (sodium hydroxide, NaOH) when reacting with water.

Explanation

Magnification refers to increasing the size of an image or object.

It is commonly used in optics, like microscopes or lenses, to enlarge small details.

Explanation

A surd is an irrational number or expression containing a square root, cube root, etc., that can't be simplified to a rational number.

Example: √2, ³√5 are surds because they involve radical signs.

Explanation

Given:

x̄ (mean) = 12

∑x (sum) = 132

The formula for mean is:

x̄ = ∑x / n

Rearrange to find n:

n = ∑x / x̄

= 132 / 12

= 11

Explanation

The Strikethrough option is found in the Font group on the Home tab in MS Word.

It allows users to draw a line through selected text.

Example:

Explanation

Work = Persons × Days = 3 × 4 = 12 person-days

With 4 persons: 12 ÷ 4 = 3 days.