The reason why the sine of a 70 degree angle is the same, regardless of the size of the triangle it's a part of, is due to the concept of similar triangles and the properties of trigonometric functions.
In trigonometry, the sine function (sin) is defined as the ratio of the length of the side opposite the given angle to the length of the hypotenuse in a right triangle. The sine of an angle is constant for that specific angle, regardless of the triangle's size or proportions.
When you have two similar triangles, it means that their corresponding angles are equal, and their corresponding sides are proportional. So, if you have two triangles, one larger than the other, with the same angle at 70 degrees, the ratio of the length of the side opposite the 70 degree angle to the length of the hypotenuse will remain the same for both triangles.
This means that for any two similar triangles with a 70 degree angle, the sine of that angle will always be the same. It's a fundamental property of trigonometry and similarity.
So, regardless of the size of the triangle, as long as the angle remains the same, the sine value for that angle will also remain the same.