fix: replace .english.md extension with .md

curriculum/challenges/english/10-coding-interview-prep/rosetta-code/vector-cross-product.md

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+---
+title: Vector cross product
+id: 594810f028c0303b75339ad2
+challengeType: 5
+forumTopicId: 302342
+---
+
+## Description
+<section id='description'>
+
+A vector is defined as having three dimensions as being represented by an ordered collection of three numbers: (X, Y, Z).
+</section>
+
+## Instructions
+<section id='instructions'>
+
+Write a function that takes two vectors (arrays) as input and computes their cross product. Your function should return <code>null</code> on invalid inputs such as vectors of different lengths.
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+tests:
+  - text: dotProduct should be a function.
+    testString: assert.equal(typeof crossProduct, 'function');
+  - text: dotProduct() should return null.
+    testString: assert.equal(crossProduct(), null);
+  - text: crossProduct([1, 2, 3], [4, 5, 6]) should return [-3, 6, -3].
+    testString: assert.deepEqual(res12, exp12);
+
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function crossProduct(a, b) {
+
+}
+```
+
+</div>
+
+
+### After Test
+<div id='js-teardown'>
+
+```js
+const tv1 = [1, 2, 3];
+const tv2 = [4, 5, 6];
+const res12 = crossProduct(tv1, tv2);
+const exp12 = [-3, 6, -3];
+```
+
+</div>
+
+</section>
+
+## Solution
+<section id='solution'>
+
+
+```js
+function crossProduct(a, b) {
+  if (!a || !b) {
+    return null;
+  }
+
+  // Check lengths
+  if (a.length !== 3 || b.length !== 3) {
+    return null;
+  }
+
+  return [
+    (a[1] * b[2]) - (a[2] * b[1]),
+    (a[2] * b[0]) - (a[0] * b[2]),
+    (a[0] * b[1]) - (a[1] * b[0])
+  ];
+}
+
+```
+
+</section>